Transport vehicles that are parked on the ground for significant periods can accumulate snow, ice or frost on their exposed surfaces in cold weather. The presence of such deposits, particularly on airfoil surfaces, is highly undesirable during aircraft takeoff and flight, since even small accumulations can result in severe deterioration of airfoil aerodynamic performance characteristics.
Ethylene glycol has long been used in aqueous solutions of various strengths for spraying onto aircraft and automotive vehicles as a deicing agent to remove snow, ice and frost deposits from glass and metal surfaces. After treatment, the glycol fluid desirably remains on the surface as a film-coating to provide continued anti-freeze protection and minimize further formation or accretion of snow, ice or frost deposits. The glycol based fluid, in various concentrations, has been used for both deicing and anti-icing functions on a wide variety of surfaces.
Generally, the glycol based fluid contains a thickening agent for surface retention.
Desirably, these deicing compositions should possess the following attributes:
(1) a flashpoint greater than 100.degree. C.
(2) hard water compatibility
(3) a freezing point below -20.degree. C.
(4) storage stability
(5) ability to form a continuous film-coating using conventional spraying devices
(6) a pour point greater than 6.degree. C.
(7) non-corrosive properties with respect to cladded or uncladded aluminum or other metal surfaces
(8) non-degradability toward painted surfaces and
(9) viscosity and rheology characteristics that promote formation of an effective, tenacious film-coating at low shear conditions while enabling the fluid coating to flow off the surface under high shear conditions.
A deicing composition which meets all of the above criteria is difficult to obtain which is evidenced by the fact that none of the prior compositions have proved to be entirely satisfactory in all of these respects. Many of the prior compositions which depend on volatile solvents possess an evaporation rate which is too rapid to effect ice release over an extended period. Such compositions are disclosed in U.S. Pat. Nos. 3,940,356 and 3,939,090. The latter composition finds limited use due to its inclusion of anionic compounds, e.g. halide and sulfur containing compounds, which have been shown to be extremely corrosive to aluminum and ferrous substrates. The deicing compositions disclosed in U.S. Pat. No. 5,118,435 depends on a complicated formulation involving blends of several polymers and requires significant amounts of thickeners for extended deicing. U.S. Pat. No. 4,698,172 employs carrageenan, a sulfated seaweed extract as a thickener which appears to have adequate deicing properties but which encounters problems in uniformity of the extract barring lengthy and expensive purification procedures. There remains a need for an economical, anti-icing composition that exhibits high pseudo-plastic rheology and which under low shear conditions is relatively insensitive to temperature changes. Another highly desirable attribute is ability to remain stable for relatively long periods of time in order to delay or avoid reapplication of the composition during aircraft departure holdovers.
Accordingly, it is an object of this invention to provide an economical deicing composition having good stability and high pseudo-plastic properties which are insensitive to temperature changes below freezing temperature.
Another object of this invention is to provide deicing composition meeting all of the above criteria which is particularly useful as a sprayed continuous coating on aircraft between flights and on automobile windshields.
These and other objects of the invention will become apparent to those skilled in the art from the following description and disclosure.